Meiosis is initiated by the programmed formation of DNA double strand breaks (DSBs). After the formation of the DSB, processing of the broken ends occurs to reveal single strand DNA that serves as the nucleation site for the homologous recombination machinery. Two RecA orthologs, Rad51 and Dmc1 cooperate to repair the DSBs in a manner that promotes chromosomal crossover formation between homologous chromatids rather than sister chromatids as in mitotic cells. This process is mediated by the Rad51 is present in both mitotic and meiotic cells while Dmc1 is specifically expressed in meiosis. Both Rad51 and Dmc1 nucleate on the single strand DNA (ssDNA) tails to form helical nucleoprotein filaments. Accessory factors known as recombination mediators promote the association of Rad51 and Dmc1 with the ssDNA. The Rad51 and Dmc1 nucleoprotein filaments invade the chromosomal homologue in search of homology. Once homology is found, a displacement loop forms followed by DNA strand exchange. The invading strand of the D-loop structure primes DNA synthesis while the second ssDNA tail is captured to form a Holliday junction. This linkage is important to keep the chromosomal homologs together until disjunction in Meiosis I. The Holliday junction is processed to form either crossovers or non-crossovers. Studies to date have unveiled only a recombination mediator activity of Mei5-Sae3 for the meiosis-specific Dmc1 recombinase. Herein, we outline strategies to determine the significance of novel protein-protein interactions involving the Mei5-Sae3 complex. In addition, we will define the contributions of the Mei5-Sae3-mediated DNA binding and protein-protein interactions in meiotic homologous recombination. The proposed studies will provide insight into the mechanism of meiotic recombination. PUBLIC HEALTH RELEVANCE: Our studies focus on the repair mechanism that processes DNA double-strand breaks initiated at the onset of meiosis to form chromosomal crossovers. Failure to form crossovers results in non-disjunction. The resulting aneuploidies result in spontaneous abortions, Down's Syndrome, Edward's Syndrome, and is associated with B-cell chronic lymphocytic leukemia and acute myeloid leukemia. The studies outlined in this application have direct relevance to cancer, mental retardation and public health.